1924, Iris Lacustris

Addisonia page 61, plate 319, 1924


Lake Dwarf-iris

Native of the region of the Great Lakes

Family Iridaceae: Iris Family

Iris lacustris Nutt. Gen. 1 : 23. 1818.
Iris cristata lacustris Dykes, Genus Iris 106. 1913.

The English name, lake-iris or lake dwarf-iris, happens to be a true appellative and a description in itself, for the circumscribed geographic area occupied by this good species is restricted to the immediate vicinity of several of the Great Lakes, or in other words its plant province is strictly the Lake Region. The botanical name is correct only in a broad sense, for the plant often grows at considerable distances from the lakes themselves.

Certain more or less conventional or stereotyped statements, casting doubt on the validity of this species, are on record. But, if differential morphological characters and an isolated geographic range mean anything in the segregation and interpretation of this species, the specific standing of Iris lacustris should not be doubted.

The flower with its accessory parts is quite distinctive. For example, the perianth-tube is narrowly funnelform — dilated from the top of the ovary to the free parts — and it is shorter than the sepals; whereas in Iris cristata the perianth- tube is slender and filiform except where dilated close to the base of the sepals and the petals, and it is much longer than the sepals. The other parts of the flower — sepals, petals, stamens, and style-branches — are also distinctive. Although May and June are the typical flowering season for this plant, in cultivation, at least, specimens flower sporadically from spring to fall.

We can, of course, easily imagine that Iris lacustris and the related species Iris cristata had a common ancestor at no remote period, geologically speaking. But they have had different histories and experiences. Where the plants of this species or its immediate progenitors existed during the glacial period or how far southward they were driven at that time we do not know. All vestiges of it have disappeared from the country south of the terminal moraine, and it has succeeded in populating or, at least, maintaining only a limited representation of its kind within an area north of the moraine in modern geologic times. It adapts itself to cultivation in various habitats far south of its natural range.

The type specimens of Iris lacnstris came from the gravelly-shores of the calcareous islands of Lake Huron, near Michilimakinak [Michilimackinac] now the city of Mackinaw. The original collector is not recorded. The specimens from which the accompanying illustration was made were sent to the New York Botanical Garden by Clarance Lown, who secured them from Mackinaw Island, Michigan. Iris lacustris is now known to grow naturally on the open sandy or gravelly shores of the three larger Great Lakes, in thickets bordering the shores, or in woods more or less remote from the lake-shore.

The lake dwarf-iris has rather slender-wiry rootstocks with tuber-like thickenings. The branches are dimorphous; the foliage ones are usually somewhat elongate, clothed with four to eight straight or nearly straight leaves with linear, often narrowly linear, nearly or quite straight blades, the lower ones scale-like, the upper two to five inches long; the flower-branches are very short with several imbricate leaves which are smaller than those of the foliage branches.

The flowers are solitary, violet-scented, partly exceeding the involucre formed by the upper leaves of the flower-stalk. The pedicel is as long as the ovary in anthesis, or shorter. The hypanthium, surrounding the ovary, is sharply three-angled, with a slight ridge on each face and a rib along each angle. The perianth-tube is one half to three quarters of an inch long, shorter than the sepals, slender-funnelform. The three sepals are cuneate, three quarters of an inch to an inch long, scarcely distinguishable into claw and blade, with a prominent crest two thirds or three fourths their length; the sharp median ridge of the crest is yellow flecked with brown, and with white and violet near the tip, the lateral ridges are white flecked with brown and violet ; the tip of the sepal is deep violet, notched, and with a dark violet band in front of the crest. The three petals are cuneate, slightly shorter than the sepals, violet, or whitish at the base, rounded or slightly notched at the apex. The three stamens are about two fifths of an inch long, with lilac filaments, deeper in shade near the tip, and white anthers mostly shorter than the filaments. The style is nearly as long as the perianth-tube. The three style-branches are broadly linear above the short-cuneate claw, about a half inch long and pale violet. The three style-appendages are semi-ovate, about one sixth of an inch long, blunt, undulate. The stigma is semicircular, not lobed, undulate. The capsules are ellipsoid, oval, or ovoid, one half to two thirds of an inch long, slightly beaked, three-angled, the lobes with a slight median ridge, each face with a shallow groove and a median line. The mature pedicels are shorter than the capsules. The seeds are obovoid, slightly inequilateral, about one twelfth of an inch long, brown, with the aril-tip curled over the top of the seed-body.

John K. Small

For more information on historic Irises visit the Historic Iris Preservation Society at

-- BobPries - 2014-12-08
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